$\begingroup$I think this was a good use of steganography. The key was that the puzzle explicitly asks to find the hidden message. The straightforward "nothing up my sleeves" surface text emphasizes that. There's no wasting time looking at the surface content, lost at what to do. The Morse code step, though easy to guess, makes it feel like a hidden code, not just an invisible message. Overall, a solid simple puzzle. My one quibble is that "Happy Christmas!" sounds weird and overlaps with the answer -- why not "Merry Christmas"? Or, some hidden message that opposes or reinterprets the surface message.$\endgroup$
– xnorDec 8 '14 at 2:04

Each symbol in "Happy​​​​‍​‌‍​‌ Christmas!" can be considered as a byte, i.e. ones and zeroes. Taking the last bit of each byte we get 01001010 01101111 which in ASCII is respectively "J" and "o". This approach is most often used with images as minor changes to the colour are really hard to detect by the human eye.